1. Field of the Invention
The present invention relates to shutter apparatus being suitably applicable to single-lens reflex cameras and of a so-called split blade type.
2. Related Background Art
Conventionally, the single-lens reflex cameras and others are often constructed using a focal plane shutter of a type in which groups of split light shielding blades are rotatably supported by parallel link mechanisms using two arm members.
The general mechanisms used in the focal plane shutters of this type are classified into a long arm type and a short arm type, depending upon the difference in a method of holding the light shielding blade groups by the arm members.
Described herein are so-called, vertically running focal plane shutters constructed to run the light shielding blade groups vertically.
First, the focal plane shutters of the long arm type are constructed in such structure that the light shielding blade groups are rotatably held on the arm members on the opposite side of the shutter aperture to the rotatable base ends of the arm members, as disclosed in Japanese Utility Model Publication No. 35-29651. For this reason, the arms become longer than the width of the shutter aperture.
Since this long arm type requires only small angles of rotation of the arm members for opening and closing of the shutter aperture by the light shielding blade groups, amounts of displacement become small in the direction perpendicular to the running direction of the light shielding blade groups during the opening and closing operation, which is advantageous to lateral downsizing of the shutter apparatus.
However, where the number of light shielding blades in each group that can be held by the two arm members was not less than 3, the long arm type had the drawback that the structure became complicated and the drawback that the inertia of the blade units became so large because of the long arms as to be disadvantageous to fast running. For this reason, the focal plane shutters of the long arm type unsuitable for increase of speed are not being used with increase in exposure time of the shutter and with increase in flash light synchronization time in recent years.
Thus the short arm type was devised in order to overcome the drawbacks of the long arm type and was substantiated in such structure that the two arm members rotatably held each group of many light shielding blades near the same side with respect to the shutter aperture as the side near the base ends of the arm members, without interposing the shutter aperture in between, though it was disadvantageous to the lateral downsizing of the shutter apparatus. In addition, in order to make the inertia smaller, it is desirable to minimize the lengths of the arms.
As an example of this short arm type, the structure and dimensional relation thereof are presented in FIGS. 21 and 22 (wherein FIG. 21 shows a running ready state and FIG. 22 a running end state).
In this shutter apparatus (which will be referred to hereinafter as the first conventional example), a leading-curtain blade unit and a trailing-curtain blade unit are mounted on a base plate 101 (shutter ground board) having a shutter aperture 101a. 
The leading-curtain blade unit is composed of five blades. Each of first arm 106 and second arm 107 on the leading curtain side has a base end rotatably supported at a shaft 101d, 101e. 
A slit forming blade 102 and covering blades 103, 104, 105, 105xe2x80x2 are rotatably coupled to the first arm 106 and the second arm 107 by blade caulking dowels 108a, 108b, 108c, 108d, 108e, 109a, 109b, 109c, 109d, 109e, and a parallel link is comprised of these two arms 106, 107, five blades, and base plate.
The trailing-curtain blade unit is composed of four blades. Each of first arm 114 and second arm 115 on the trailing curtain side has a base end rotatably supported at a shaft 101f, 101g. 
A slit forming blade 110 and covering blades 111, 112, 113 are rotatably coupled to the first arm 114 and the second arm 115 by blade caulking dowels 116a, 116b, 116c, 116d, 117a, 117b, 117c, 117d, and a parallel link is comprised of these two arms 114, 115, four blades, and base plate.
In each of the leading curtain and the trailing curtain, the blade caulking dowels are successively arranged so as to draw a gentle arc and the first arm and the second arm are juxtaposed near to each other in a superimposed state in which the blade unit opens the shutter aperture.
In each of the leading curtain and the trailing curtain, neither of the blade 105xe2x80x2, 113 with the smallest travel (moving distance) and the blade 105, 112 with the second smallest travel (moving distance) is provided with a light shielding piece extending generally in the blade running direction, near the coupling portion to each arm.
For this reason, each of the blades 104, 111 with the third smallest travel, and the blade 103 with the fourth smallest travel in the leading curtain is provided with a light shielding piece (103a, 104a, 111a indicated by hatching in the drawings).
Further, in the superimposed state in which the blade group of the leading curtain or the trailing curtain opened the shutter aperture 101a, the light shielding piece of the blade 104, 111 with the third smallest travel (104a, 111a indicated by hatching) was not located between the coupling portions 109d, 109e; 117c, 117d to the second arm, of the blade 105xe2x80x2, 113 with the smallest travel and the blade 105, 112 with the second smallest travel.
From the viewpoint that it was hard to achieve the downsizing by the parallel link mechanisms using two arms, the following was proposed as a shutter apparatus downsized by adding the third auxiliary arm.
The shutter apparatus disclosed in Japanese Utility Model Publication No. 6-26896 (which will be referred to hereinafter as the second conventional example) was constructed in such structure that in the blade superimposed state the coupling portions on the first and second arms for coupling and supporting the slit forming blade were accommodated in a storage region present between the finder and the aperture window and that the third arm supporting the other covering blades was located outside the region, thereby decreasing the lateral contour size of the shutter apparatus.
This apparatus is constructed in the structure in which each arm is made slim in order to place the three arms in the narrow space and, in the superimposed state in which the blade group opens the shutter aperture, the first arm and the third arm are arranged so that the center of rotation of the base end of the third arm is interposed between the center of rotation of the base end of the first arm and the caulking dowel of the third covering blade and so that the caulking dowel of the third covering blade on the first arm is interposed between the center of rotation of the base end of the third arm and the caulking dowel of the third covering blade.
Although not referred to in this official gazette, the light shielding piece projecting on the almost opposite side to the blade running direction is provided near the coupling portions to the first and second arms in the blade with the second smallest travel, as shown in the drawings of the official gazette.
However, the light shielding piece provided in the blade with the third smallest travel is not located between the coupling portions to the second arm of the blade with the smallest travel and the blade with the second smallest travel in the superimposed state in which the blade group opens the shutter aperture.
Further, Japanese Utility Model Publication No. 7-25787 discloses the shutter apparatus also having the third arm (which will be referred to hereinafter as the third conventional example) wherein, in order to prevent exposure unevenness caused when the parallel state of the slit forming blade is degraded by deflection, swingback, play, etc. of the slit forming blade, the parallel link is composed of the first arm, the second arm, and a plurality of covering blades and the first arm and the third arm support the slit forming blade without constituting a parallel link.
Although not referred to in this official gazette, either, the light shielding pieces projecting on the almost opposite side to the blade running direction are formed near the coupling portions to the first and second arms in the blade with the smallest travel and the blade with the second smallest travel, as shown in the drawing of the embodiment.
However, the light shielding piece provided in the blade with the third smallest travel is not located between the coupling portions to the second arm of the blade with the smallest travel and the blade with the second smallest travel in the superimposed state in which the blade group opens the shutter aperture (this shutter apparatus will be referred to hereinafter as the third conventional example).
As a downsized shutter apparatus in another structure (which will be referred to hereinafter as the fourth conventional example), for example, Japanese Utility Model Publication No. 57-57367 discloses the apparatus having the slit forming blade and covering blades driven by the parallel link mechanism using two arms, wherein for supporting one end of the first covering blade subsequent to the slit forming blade, a blade supporting member is rotatably supported on one arm to increase degrees of freedom for design of the supporting position of the first covering blade, thereby preventing interference between the blade and the supporting position in the downsized structure.
The supporting portion of the first covering blade is interposed between the support point on the arm of the blade supporting member and the support point on the arm of the second covering blade in the superimposed state in which the blade unit opens the shutter aperture.
Although not referred to this official gazette, the light shielding piece extending on the almost opposite side to the blade running direction is provided near the coupling portion to the first and second arms in the blade with the smallest travel, in the drawings.
However, the blade with the third smallest travel (slit forming blade 3a) is not provided with the light shielding piece extending on the almost opposite side to the blade running direction near the coupling portions to the two arms.
Neither of the second, third, and fourth conventional examples described above is of such structure that the coupling portions to the arms of the blade with the smallest travel and the blade with the second smallest travel in the blade groups are located outside an extension of the width of the blade main body portion in the blades.
In general, for downsizing of the shutter apparatus (particularly, lateral downsizing), the smaller the number of split blades in each blade group, the smaller the number of coupling portions between the arms and the blades and the smaller the area occupied by the coupling portions, which is advantageous to the downsizing.
On the other hand, the smaller the number of blades, the smaller the mutual overlapping amount of the blades for light shielding of the shutter aperture of predetermined size, which will make it hard to ensure the light shielding performance.
In the first conventional example, if the length of the arms is decreased in order to achieve the downsizing, since the number of blades in the leading curtain is as large as five, the intervals of the blade caulking dowels will become smaller while being successively arranged to draw a gentle arc and degrees of freedom will be decreased for the rotatable supporting positions of the covering blades, so as to cause interference in the blade unit (for example, in FIG. 22, interference between the circumference of the base end 106b of the first arm 106 and the circumference of the second arm 107 or the covering blade 105xe2x80x2 around the blade caulking dowel 109e, interference between the circumference of the first arm 106 around the blade caulking dowel 108e and the circumference of the second arm 107 or the covering blades 104, 105 around the blade caulking dowels 109c, 109d, etc.), which will not allow increase in operating angles of rotation of the arms.
The reason for this is that as long as the size of the shutter aperture in the blade running direction is fixed, the decrease in the length of the arms in the parallel link requires increase in the operating angles of rotation of the arms in order to move the blades by the determined distance.
In addition, the first conventional example has the disadvantage that it becomes difficult to maintain the overlapping amount of the slit forming blade and the covering blades during expansion of the blades closing the shutter aperture. Accordingly, the first conventional example failed to downsize the apparatus largely.
On the other hand, let us suppose the trailing-curtain blade unit of the four blade structure is also applied to the leading-curtain blade unit. The overlapping amount of the blades is small, about 2 mm, during expansion of the trailing curtain, as shown in FIG. 22. Even if the width of each blade is increased in the range allowed by the blade storage space in the superimposed state of the leading curtain, the intervals of the blade caulking dowels will also be short while the blade caulking dowels are successively arranged so as to draw a gentle arc, as in the case of the foregoing blade unit of the five blade structure. This will decrease degrees of freedom for the rotatably supporting positions of the covering blades from constrictions on the arrangement of the blade caulking dowels, so as to cause interference in the blade unit (for example, in FIG. 21, interference between the circumference of the base end 114b of the first arm 114 and the circumference of the second arm 115 or the covering blade 113 around the blade caulking dowel 117b, interference between the circumference of the first arm 114 around the blade caulking dowel 116d and the circumference of the second arm 115 or the covering blade 112 around the blade caulking dowel 117c, etc.), which allows increase of only about 1 mm more on the opposite side to the blade running direction. Therefore, the conventional technology failed to ensure the desired blade overlapping amount of 4 mm and also failed to downsize the apparatus largely (reference should be made to (6) described hereinafter as to the description concerning the arrangement of the blade caulking dowels).
In both the leading curtain and the trailing curtain, neither of the blade 105xe2x80x2, 113 with the smallest travel and the blade 105, 112 with the second smallest travel is provided with the light shielding piece extending in the blade running direction near the coupling portion to the arms. The reason for it is that the distance is large between the coupling portions to the arms of the blade 105xe2x80x2, 113 with the smallest travel and the blade 105, 112 with the second smallest travel and the edge 101axe2x80x2 on the blade root side in the shutter aperture 101a and even with provision of the light shielding piece this light shielding piece does not enter the shutter aperture 101a and is thus useless (unnecessary), which means that the downsizing is not implemented by that degree in the direction perpendicular to the blade running direction.
On the other hand, since in the first conventional example the light shielding pieces (103a, 104a, 111a indicated by hatching) are provided in the blades 104, 111 with the third smallest travel, and the blade 103 with the fourth smallest travel in the leading curtain, which have the coupling portions to the arms at the positions near the shutter aperture 101a, the mass increases in the blades with the large travels located on the distal end side of the arms.
Accordingly, the center of gravity of each blade unit is shifted to the side where the radius of rotation is large from the base ends of the arms, which posed the problem that the inertia of the blade units was increased.
Further, in the first conventional example, in the superimposed state of the blade group of the leading curtain or the trailing curtain, the light shielding piece (104a, 111a indicated by hatching) of the blade 104, 111 with the third smallest travel is not located between the coupling portions (109d and 109e; 117c and 117d) to the second arm of the blade 105xe2x80x2, 113 with the smallest travel and the blade 105, 112 with the second smallest travel, which also indicates that the downsizing is not implemented in the direction perpendicular to the blade running direction by shortening the lengths of the arms and increasing the angles of rotation of the arms.
In the foregoing second conventional example (Japanese Utility Model Publication No. 6-26896), the third arm was added for supporting the covering blade group, which caused the disadvantages that the structure became more complicated, the operational resistance also became higher, and the inertia of the blade units became larger than in the case of the general parallel link mechanisms with two arms as in the first conventional example.
Since the three arms were placed in the small space, each arm became slim, which also caused the disadvantage that the strength of the arms themselves was low.
In addition, since in the superimposed state of the blades the coupling portions on the first and second arms supporting the slit forming blade were accommodated in the storage region present between the finder and the aperture window, the coupling distance became short on the slit forming blade of the parallel link, which also caused the disadvantage that it was difficult to maintain the parallelism of the exposure slit.
Further, since in the second conventional example the coupling portions of the blade 6xe2x80x2, 106 (which are reference numerals in No. 6-26896; the same will also apply to the description below in this paragraph) with the second smallest travel to the first and second arms 8xe2x80x2, 10xe2x80x2; 108, 110 was placed within the root width of the strap-shaped blade main body portion so as, to make the supporting portions close to each other, the light shielding piece was large, which lowered the function of light shielding of the shutter aperture by the blade 7xe2x80x2, 107 with the smallest travel.
For this reason, the mass increases in the blades with the larger, even a little, travels located on the distal end side of the arms with respect to the blade with the smallest travel. Accordingly, the center of gravity of the blade unit was shifted to the side where the radius of rotation was large from the base ends of the arms, which caused the disadvantage that the inertia of the blade units became large.
In the foregoing third conventional example (Japanese Utility Model Publication No. 7-25787), the fundamental structure is the same as in the first embodiment described in the second conventional example, and thus it had the drawbacks of the complicated structure due to the three arms, the increase of operational resistance, and the large inertia of the blade units, the drawback of the low strength of the arms themselves, and the drawback of the large light shielding pieces, because the coupling portions of the blade 2c (which is the reference numeral in No. 7-25787; the same will also apply to the description below in this paragraph and in the next paragraph) with the second smallest travel to the first and second arms 11, 12 were placed within the root width of the strap-shaped blade main body portion so as to make the supporting portions close to each other.
In addition, the coupling portions of the blade 2d with the smallest travel to the first and second arms 11, 12 were also placed within the root width of the strap-shaped blade main body portion and the light shielding portion with the slim root was provided in the shape completely independent of the blade portion and the coupling portion, which resulted in the drawback that the light shielding piece was easy to break at the root.
In the foregoing fourth conventional example (Japanese Utility Model Publication No. 57-57367), the weight of the blade supporting member and the blade was exerted on the supporting portions on the arms supporting the blade supporting member, and thus there was the disadvantage that the durability was poor, particularly, at the supporting portions.
The addition of the blade supporting member also caused the disadvantages that the structure became more complicated, the operational resistance was also greater, and the inertia of the blade units became larger than in the case of the general parallel link mechanisms with two arms as in the first conventional example.
Accordingly, the above conventional examples were disadvantageous to the fast running of the blade units and it was thus difficult, for example, in cameras to implement the exposure time shorter than {fraction (1/4000)} sec or implement the strobe synchronization time shorter than {fraction (1/200)} sec.
The shutter charge energy necessary for implementing the same curtain speed increased, which increased the size of the camera and which was disadvantageous to increasing the frame speed during continuous shooting.
A first object of the present invention is to provide shutter apparatus downsized, particularly, in the size in the direction perpendicular to the running direction of the light shielding blades, maintaining the sufficient blade overlapping amount for light shielding, keeping the inertia of the blade units small by some means for the mounting positions of the light shielding pieces, having high operation efficiency and excellent durability, and being suitable for fast operation.
One aspect of the present invention discloses a shutter apparatus comprising:
a shutter base plate having a shutter aperture;
a first arm member which rotates around a center of rotation at a first axis, relative to the shutter base plate;
a second arm member which rotates around a center of rotation at a second axis, relative to the shutter base plate; and
a plurality of shutter blades,
wherein each of the plurality of shutter blades is coupled to the first and second arm members, wherein the first and second arm members rotate around their respective axes whereby the plurality of shutter blades run over the shutter aperture, wherein each shutter blade has a blade main body portion extending in a direction perpendicular to a running direction thereof, and wherein a first shutter blade with a smallest running travel comprises a light shielding portion projecting in the running direction on the coupling portion side to the first and second arm members and arranged to effect light shielding of the shutter aperture.
Particularly, the apparatus satisfies the following condition:
L1 greater than W1,
where W1 is a length in the running direction, of the blade main body portion of the first shutter blade and L1 is a projection length of the light shielding portion from the blade main body portion.
Further, a second shutter blade with a second smallest running travel out of the plurality of shutter blades comprises a second light shielding portion projecting in the running direction on the coupling portion side to the first and second arm members and arranged to effect light shielding of the shutter aperture.
The apparatus satisfies the following condition:
L2 greater than W2,
where W2 is a length in the running direction, of the blade main body portion of the second shutter blade and L2 is a projection length of the second light shielding portion from the blade main body portion.
Another aspect of the invention discloses a shutter apparatus comprising:
a shutter base plate having a shutter aperture;
a first arm member which rotates around a center of rotation at a first axis, relative to the shutter base plate;
a second arm member which rotates around a center of rotation at a second axis, relative to the shutter base plate; and
a plurality of shutter blades,
wherein each of the plurality of shutter blades is coupled to the first and second arm members, wherein the first and second arm members rotate around their respective axes whereby the plurality of shutter blades run over the shutter aperture, wherein each shutter blade has a blade main body portion extending in a direction perpendicular to a running direction thereof, and wherein a first shutter blade with a second smallest running travel comprises a light shielding portion projecting in the running direction on the coupling portion side to the first and second arm members and arranged to effect light shielding of the shutter aperture.
Particularly, the apparatus satisfies the following condition:
L2 greater than W2,
where W2 is a length in the running direction, of the blade main body portion of the first shutter blade and L2 is a projection length of the light shielding portion from the blade main body portion.
Further, a second shutter blade with a smallest running travel out of the plurality of shutter blades comprises a second light shielding portion projecting in the running direction on the coupling portion side to the first and second arm members and arranged to effect light shielding of the shutter aperture.
The apparatus satisfies the following condition:
L1 greater than W1,
where W1 is a length in the running direction, of the blade main body portion of the second shutter blade and L1 is a projection length of the second light shielding portion from the blade main body portion.
Further features of the invention will become apparent from the drawings and the description which will follow.